The present invention relates to the stabilization of a gimbaled pointing mirror and, in particular, to a simplified and accurate system therefor.
It is important to stabilize a pointing mirror against angular base motions with respect to an inertial reference, such as a field of view, especially when the pointing mirror is mounted on a moving vehicle. Movements imparted to the vehicle are transmitted to the mirror through rotations about any or all of the x, y, and z or i, j, and k axes.
Prior stabilized pointing mirror designs utilized two rate-integrating, single-degree-of-freedom gyroscopes, which were attached to a separately gimbaled reference inertia. While operating adequately to stabilize the mirror, these prior designs required a relatively large number of mechanical parts, which both increased the complexity and cost of the pointing mirror system. In addition, as the number of electrical and mechanical parts increased, the possibility of error also increased, thereby decreasing its pointing accuracy.
Such prior systems are exemplified in "The Infrared Handbook" by Wolfe and Zissis, editors, prepared by the Infrared Information and Analysis (IRIA) Center, Environmental Research Institute of Michigan for the Office of Naval Research, Department of the Navy, Washington, D.C., First Edition 1978, Revised Edition 1985, in Chapter 22 entitled "Tracking Systems" pages 22-1 et seq., specifically, pages 22-9 and 22-10. There, the pointing mirror is secured mechanically by belts or bands to a balanced inertia band drive and a gyroscopically stabilized reference. When either or both of the balanced inertia band drive and gyroscopically stabilized reference are balanced, the mirror is balanced. However, that structure is mechanically and electronically complex, entails additional structure which prevents attainment of high bandwidth control or closure of the electro-mechanical loop from the mirror to the electronics and back to the mirror. As is known, the higher the bandwidth, the higher the frequencies that can be attenuated. However, as stated above, as the mechanical parts become more complex, it becomes more difficult to get stable loop closure. The problem is primarily in the mechanics which do not have sufficient structural integrity, that is, the ability to respond to input demands, which detracts from stable loop closure and results in oscillation of the mirror.